Wind transportation

Question 1

Name three ways that sand can be transported by wind

Answer 1

Surface creep
Saltation
Suspension

Question 2

Describe wind deposition

Answer 2

Deposition takes place when wind velocity falls below critical value. Velocity vairs according to size of sand particle.

Question 3

Where is sand deposited?

Answer 3

In sheltered areas protected from the wind. leeward side of rocks eg

Question 4

Whats is surface creep?

Answer 4

When larger sand particles are rolled along the desert floor

Question 5

Whats is Saltation?

Answer 5

Sand particles move in a series of leaps as they are picked up by a gust of wind before being dropped downwind

Question 6

What is Suspension?

Answer 6

fine sands and clays may be picked up and carried considerable distances. Common when high velocity winds create sandstorms

Question 7

Give me an example of suspension

Answer 7

Sand form the Sahara transported to Florida, >8000 km away.

Question 8

When is a sand dune NOT solely a depositional process?

Answer 8

when it is mobile and therefore a type of flow- an ongoing surface creep

Question 9

When is a sand dune a depositional process?

Answer 9

when it is fixed and largely static it is truly depositional and represents a temporary store in balance at the time but vulnerable to change if environmental conditions change.

Question 10

Define mechanical or physical weathering

Answer 10

Gradual disintegration of rocks without chemical change.

Question 11

What is the most important type of mechanical weathering?

Answer 11

Thermal fracture in a desert environment.

Question 12

What is thermal fracture?

Answer 12

ntense temperatures fluctuations cause rock to expand and contract. Moisture (from dew) promotes this process.

Question 13

What is thermal fracture dependent on?

Answer 13

Colour, lithology ( rock type) and geological structure of the rocks

Question 14

Name 4 types of Thermal fracture

Answer 14

granular disintegration
block separation
shattering
exfoliation

Question 15

What is granular disintegration

Answer 15

granular rocks tend to crumble into individual grains of sand. the coloured minerals in granite are heated at different rates which facilitates the break of rocks

Question 16

What two minerals are commonly found in granite?

Answer 16

black Mica and white quartz

Question 17

Which types of rock are prone to granular disintegration?

Answer 17

granite and sandstone

Question 18

What is block separation?

Answer 18

if rocks have a clear pattern of joints and bedding plains they are prone to breaking into blocks

Question 19

Which types of rock are prone to block separation?

Answer 19

Sedimentary rocks such as limestone

Question 20

What is shattering?

Answer 20

rocks that do not have separate grains or joints tend to shatter to form angular fragments.

Question 21

Which type of rock is prone to shattering?

Answer 21

Igneous rock such as basalt

Question 22

What is exfoliation?

Answer 22

The outer skin of the rock peeling away as a result of repeated heating and cooling. Rocks are poor heat conductors.

Question 23

Which types of rock are prone to exfoliation?

Answer 23

Exposed granite or sandstone

Question 24

What is salt crystallisation?

Answer 24

Rain dissolves salts in the soil. The high rate of evaporation draws water to the surface by capillary action and salt crystals are deposited on the ground surface. over time these crystals may grow and expand causing stresses that eventually break up rocks.

Question 25

What is frost shattering.

Answer 25

Water often in the form of dew freezes and expands in cracks and pores in the rocks. Repeated cycles cause the rocks to shatter.

Question 26

Where does frost shattering occur?

Answer 26

Temperature must be below 0 degrees centigrade. Common in upland or mountainous regions - middle east and northern fringes of Sahara desert.

Question 27

What is chemical weathering?

Answer 27

Rocks that change as a result of chemical action (usually in the presence of water).

Question 28

What indicates chemical weathering in hot deserts?

Answer 28

flaking or pitting of rocks. underground deposits of rock salt as can be found in the Atacama desert.

Question 29

Which chemical weathering process is most effective in cold climates?

Answer 29

carbonation - the dissolving of limestone by acidic rain water

Question 30

Why is weathering more intense in high temperatures?

Answer 30

because some chemical reactions are enhanced by heat

Question 31

What are the main sources of water in deserts?

Answer 31

Exogenous rivers
Endoreic rivers
Ephemeral rivers
Episodic flash floods

Question 32

What are exogenous rivers?

Answer 32

Rivers that have their source outside the desert region. they have suffucuent water to flow despite high rate of evaporation

Question 33

Name some exogenous rivers?

Answer 33

Colorado, Indus, Nile

Question 34

What are endoreic rivers?

Answer 34

rivers that flow into a desert but terminate in a lake of inland sea

Question 35

Name an endoreic river

Answer 35

River Jordan which drains into the Dead Sea

Question 36

What is an ephemeral river?

Answer 36

rivers or streams that flow intermittently. they may flow after storm event or fed by snowmelt. They can be powerful sources of erosion and flow rates can vary dramatically.

Question 37

What are episodic flash floods?

Answer 37

infrequent rainfall events that involve torrential convectional storms releasing large amounts of water in a short space of time.water can flow as a sheet over the sun baked land ( sheet flooding) or can be confined in a channel (channel flash flooding)

Question 38

What is one result of episodic flash floods?

Answer 38

large amounts of sediment ar washed out of the mountains to be deposited as vast alluvial plains on the lowlands below.

Question 39

name 6 causes of desertification

Answer 39

over-cultivation
overgrazing
over irrigation
population increase
firewood
tourism

Question 40

explain how overcultivation leads to desertification

Answer 40

intensive farming decreases soil fertility. lack of organic matter makes soil more likely to be washed or blown away

Question 41

explain how overgrazing leads to desertification

Answer 41

if the land exceeds its carrying capacity the vegetation and soil will suffer

Question 42

explain how overirrigation leads to desertification

Answer 42

if plants are over irrigated the salts can be dissolved in the soil and form a salty crust when the water evaporates ( salinisation). This created impermeable, infertile soil.

Question 43

explain how population increase leads to desertification

Answer 43

if the rate of population increase exceeds the rate of food production it puts additional pressure on the land to be productive.

Question 44

explain how firewood leads to desertification

Answer 44

land quickly becomes stripped of the few trees as people rely on firewood for cooking. This exposes the soil to wind and rain leading to soil erosion.

Question 45

explain how tourism leads to desertification

Answer 45

high concentration so safari buses in countries such as Kenya leads to damage of vegetation, leading to soil erosion

Question 46

What is the population of Africa’s Sahel region and how does it changeover time?

Answer 46

it is estimated at 260 million and doubles every 20 years. this is a 3% growth per year.

Question 47

How does desertification affect ecosystems?

Answer 47

Loss of nutrients - due to over exploitation by agriculture eaves soils impoverished –> loss of biodiversity
Loss of topsoil - the most nutritious horizon, due to wind and rain
Increased salinity if irrigation is used
Water sources become depleted - plants and animals die
As plants die animals have to migrate to find other suitable veegetation